Powertrain, generic · Fuel and air metering

P0170 Fuel Trim Bank 1

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

With closed-loop control the engine module corrects the injected fuel using the oxygen sensor: short-term fuel trim reacts within fractions of a second, long-term trim stores a learned base correction per load and speed range. Positive values mean fuel is being added because the mixture was lean, negative values mean fuel is being removed; around ±10 % is normal. P0170 is the older, direction-neutral code for 'mixture adaptation of bank 1 out of range'; whether lean or rich has to be read from the trim values. Users are Mercedes-Benz petrol engines, which often set P0170/P0173 instead of P0171–P0175 – a Mercedes-Benz magazine for independent workshops reports that cleaning or replacing the air flow sensor most often cures it – and Ford's 6.7 litre diesel, where it flags a fuel quantity error above 15 % in either direction from its fuel mass observer. GM and Ford petrol engines do not use it. Two trips.

Likely causes

Air flow sensor dirty or drifting
Air leak or crankcase ventilation leaking
Injection quantity error (diesel: injector drift, rail pressure sensor; petrol: injectors, fuel pressure)
Oxygen or NOx sensor offset

Symptoms

  • Check engine light on (after two drive cycles)
  • Rough idle or hesitation
  • Higher consumption
  • Often no symptoms

Repair estimate

DifficultyMediumDIY possible
Parts and labour€20–600
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

oxygen sensor bank1 sensor1mass air flow sensorfuel systemintake manifold

Related codes

P0173P0171P0172P0101P0263

References: law.cornell.edu, fordservicecontent.com, automotivetechinfo.com.